The objective of this proposal is to enable the microsurgeon to improve the viability rate and function of replanted extremities and free vascular tissue transfers. Emphasis will be placed on understanding the cause of the "no flow" and "no reflow" phenomena In order to minimize the occurrence of these events and optimize the success rate of such procedures. We define "no flow" as a lack of blood flow across the anastomotic site despite technically satisfactory anastomosis, and "no reflow" as the failure of blood to perfume the distal tissue and return through the veins after successfully traversing the anastomosis site. Despite our identification of a number of factors involved in each of these events, an unacceptably high rate of failure of replanted and transferred tissues continues to exist. Our previous studies have shown that ischemia, hypothermia, denervation, intimal and internal elastic lamellar injury and surgical anastomosis are primarily responsible for the pathogenesis of "no flow" and "no reflow." This grant proposal is divided into two major areas of emphasis. The interaction of known factors in the occurrence of the "no flow" phenomenon at the arterial level will be evaluated to determine the effect of various combinations of ischemia, hypothermia, and anastomosis on the degree of endothelial injury and thrombus formation produced by a controlled crush injury. The effect of fragmentation of the internal elastic lamella of the femoral artery on patency and thrombus formation will also be examined following ischemia and/or hypothermia and/or surgical anastomosis. Concurrently, the interaction of pharmacologic agents and physiological conditions known to participate in the pathogenesis of the "no reflow" phenomenon at the capillary level will be thoroughly investigated using a rat cremaster muscle model. The Incidence of microcirculatory failure is now believed to be largely due to the oxygen free radical production that occurs during the period of ischemia. We propose to proceed during the next grant period with our experiments examining the effects of the oxygen free radical scavengers and their possible benefit during replantation and free tissue transfers. Additionally we will evaluate the importance of calcium channel blockers and their use to stabilize the cell environment and prevent the deleterious effects of ischemia on calcium homeostasis. This research will benefit all areas of medicine that encounter the need for optimal tissue preservation, and prevention of ischemia-induced tissue damage.